STUDIES ON THE SALT TOLERANCE IN KOREAN R ICE CULTIVARS .1. MECHANISMOF SALT TOLERANCE IN DRY-MATTER PRODUCTION AND LEAF PHOTOSYNTHESIS

Reduction of relative growth rate (RGR) due to the NaCl treatment was examined in the seedlings of six Korean rice cultivars which had been reported to be different in salt tolerance on the level of grain yield . On the level of RGR, three of the cultivars were identified as salt tolerant, and the remaining three were identified as the sensitive cul tivars. Further analysis of RGR indicated that the reduction of RGR by NaCl treatment was attributed in large part to the reduction of the n et assimilation rate (NAR) rather than to that of the leaf area ratio (LAR). Leaf photosynthesis which is closely related with NAR, was also reduced by NaCl treatment in salt sensitive cultivars to a greater ex tent than tolerant cultivars. Ribulose-1, 5-bisphosphate carboxylase/o xygenase (Rubisco) content was determined in a tolerant cultivar, Han- Kang-Chal, and a sensitive one, Dong-Hae. Han-Kang-Chal showed a small er decrease of Rubisco content per absorbed Na in the NaCl-treated lea ves. This indicates that degradation of Rubisco by absorbed Na is slow er in tolerant cultivars than in sensitive cultivars. Moreover, Han-Ka ng-Chal showed a larger decrease in osmotic potential in the NaCl trea ted leaves, suggesting that osmotic adjustment was developed under sal t stress conditions in a tolerant cultivar.